1. Field of the Invention
The present invention relates to cooking or fume generating surface exhausts, and more particularly to exhaust systems including boundary layer injection.
2. Description of the Prior Art
The use of exhausts to evacuate fumes developed over various fume-producing processes has been known in the past. Most typically, such exhausts are formed in the manner of range hoods which are either vented to the exterior of the home or filter the fumes and return the air back into the kitchen. Where large cooking facilities or other large fume-producing processes are involved and therefore large attendant volumes of associated fumes are formed, such as in restaurants and other commercial food dispensing facilities, the typical range hood or the exhaust system associated therewith incorporates blowers which evacuate the air below the range hood and exhaust such air into the exterior atmosphere.
Typically, such prior art exhaust systems rely on the natural convection currents of the warm fumes in order to direct the fumes into the hood area. Such arrangements, while adequate for non-commercial use, are not sufficiently effective in commercial food applications. More specifically, where commercial food production takes place, large quantities of ambient, tempored room are drawn from the kitchen thereby producing heavy air turbulence and drafts and also causing discomfort to employees working in the area. Accordingly, an exhaust system which does not efficiently evacuate all of the fumes associated with cooking both raises the temperature in the vicinity of the cooking range and therefore raises the attendant personal discomfort and furthermore allows a part of the fumes to bypass the hood or spill over into the working area. This continued accumulation of both heat and fumes within the working environment of hired personnel is then necessarily corrected by various air conditioning systems which are both expensive to install and require large amounts of power when in use.
An additional problem associated with conventional range hoods, whether adapted for commercial or for non-commercial use, is that large amounts of cooking vapors have a tendency to collect on the interior surfaces thereof to the point where eventually the collected matter reaches a point posing a real hazard of fire. More particularly, in the conventional convection flow range hoods most of the vapors or particulate matter collects on the interior surfaces of the hood closest to the cooking surface and an incident of fire on the range surface can ignite these deposits, which then can self-propagate the flame into the interior of the stack.
It is typically the feature of the thin-walled structure of the hood itself that is the most pronounced cause of such fires. Specifically, this thin-walled structure presents a low thermal mass and is therefore easily warmed up to a point above the combustion point of the deposits on the surface thereof. In the prior art the U.S. Pat. No. 3,400,649 dated Sept. 10, 1968, describes an exhaust system showing rear boundary air injection but does not show the more complete air injection system as set forth in the present application for patent.